Joanna (Keira Knightley) and Michael Reed (Sam Worthington) are in a successful and happy relationship. They are moving along in their lives together until Joanna meets Laura (Eva Mendes), the stunningly beautiful work colleague whom Michael never mentioned. While Michael is away with Laura on a business trip, Joanna runs into an old but never quite forgotten love, Alex (Guillaume Canet). As the night progresses and temptation increases, each must confront who they really are.